The invention is in the particular field of equipment for transferring electrical components to printed circuit boards automatedly for assembly therewith. However, it is contemplated that the structure is readily adaptable to other electrical component handling equipment and to similar robotic applications of a more general nature.
Such transferring generally involves cyclical moving of a pick and place head such as a vacuum spindle from a "picking" station at which an electrical component is picked up to a "placing" station at which the component is placed down at a selected location on the face of the circuit board. The X-Y positioning of the selected circuit board location relative to the vacuum spindle is accomplished by moving either the circuit board or the spindle in X and Y, or moving both in at least one of the directions.
Devices for repositioning the pick and place head in X and Y with the speed, accuracy, reliability, and repeatability required by the industry have involved mounting the head for movement along and on precision ground ways (in the X direction), which are supported at each end for movement perpendicular thereto (in the Y direction), with these movements being along the axes of precision ground lead screws (defining the X and Y axes) via mating ball nuts. Inherent to these devices are the complicated and costly drive mechanisms necessary to accomplish the linear travel of an axis with the precision required.
It is also known in the prior art to use harmonic drive gearing for a reducing unit in precision X-Y positioning systems. However, such units are limited to an input of only about 2000 rpm and can provide a low end reduction ratio of only about 50:1. These limits compare unfavorably to a prototype of the instant invention which accepted an input of 4800 rpm and provided the low end reduction ratios of 10:1-15:1 which are desirable for servos. Further, the higher inertia of the harmonic drive unit causes more energy to be consumed in the power train. The necessary reduction would be very difficult to achieve with the harmonic drive and, if achievable, would be much more expensive than that of the instant invention.
Thus, it is an object of the invention to provide reliable, high accuracy X-Y positioning of a moveable linear axis without the need for the precision required of the component parts of prior art devices. This and other objects of the invention will become more apparent from the following detailed description, drawings, and claims of the invention.